What the OGTT curve is tracking
The oral glucose tolerance test measures how blood glucose responds to a standardized sugar load, usually 75 grams of glucose for adults, with blood drawn at intervals such as 0, 30, 60, 90, and 120 minutes. In a person with normal glucose handling, the curve rises after the drink and returns toward baseline within about two hours as insulin moves glucose into tissues.
An impaired curve climbs higher and clears more slowly, reflecting reduced insulin sensitivity or insufficient insulin response, while a diabetic-range curve stays elevated at the two-hour mark.
How clinicians read the thresholds
Diagnostic categories are commonly based on the fasting and two-hour values. Widely used cutoffs place a two-hour glucose below about 7.8 mmol/L (140 mg/dL) in the normal range, roughly 7.8 to 11.0 mmol/L (140 to 199 mg/dL) as impaired glucose tolerance, and 11.1 mmol/L (200 mg/dL) or higher as the diabetic range, with confirmation often required.
Exact thresholds and protocols differ between guidelines and laboratories. This is general educational information, not a diagnosis; interpretation of any glucose result should be done by a qualified clinician.